The present invention relates to the control of zebra mussels (Dreissena polymorpha) in aqueous systems by utilizing as a molluscicide an effective amount of a composition comprising: a) a water-soluble quaternary dialkyl diallyl ammonium polymer (polyquat); and b) a dedecyl dimethyl ammonium halide.
Zebra mussels recently have been discovered in the Great Lakes. It is believed that these mollusks were carried to North America in the ballast of ships from Europe. Zebra mussels reproduce quickly, and attach to virtually any hard surface in contact with an aqueous system in which they are present. These organisms are particularly troublesome to industrial and municipal users of fresh water, as zebra mussels can quickly foul water intakes and process equipment.
Zebra mussels fall within the class Bivalvia of the phylum Mollusca. The mature mussels are characterized by threadlike tenacles (byssal threads) which enable them to attach themselves to virtually any hard underwater surface. Since a zebra mussel is particularly adherent to the shell of another zebra mussel, these mollusks tend to "stack up", one upon another, so that they can completely clog intake orifices. Additionally, the threads enable the mussels to affix themselves to a surface which is positioned in any plane relative to horizontal. Thus, unlike other mollusks such as Asian clams (Corbicula), zebra mussels are found on the ceilings, vertical surfaces and floors of under water equipment.
On a daily basis, vast quantities of water are removed from rivers, lakes and streams for potable water use and for use in a variety of industrial processes. The greatest industrial use of water is for cooling purposes, and the greatest nonconsumptive industrial demand for water as a heat transfer medium comes from the steam-electric generating industry. Also, municipalities draw water for public consumption.
Source water supports an abundance of biological life forms, many of which cannot be removed from the water before it is used. While some of these biological life forms may not adversely affect municipal or industrial treatment processes, zebra mussels are biofouling organisms which have become a severe problem in North America in a very short time. These mussels foul intake piping and equipment surfaces in municipal water treatment plants and in industrial water systems.
It is believed that zebra mussels did not become prevalent in Lake Erie until late 1988 or 1989. They are now rapidly spreading into Lake Michigan and into the rivers of the Midwest and Northeast. In a relatively short time, they can reach population densities in excess of 30,000 mussels per square meter. For this reason, zebra mussels can completely shutdown municipal and industrial systems which rely on fresh water infested with zebra mussels. It is believed that zebra mussel fouling will eventually threaten virtually every domestic municipal, utility and industrial user of fresh water that draws its supply from a source which is in fluid communication with the Great Lakes.
Zebra mussel fouling of such equipment as intake piping and steam condensers can be extremely troublesome. Immature or small mussels are easily drawn through intake screens. Once inside a system, they can lodge anywhere. The problem is made worse by the fact that, in the larval state, zebra mussels are carried by flowing water throughout treatment and/or process systems.